24 MORPHOLOGY AND CULTURE OF MICROORGANISMS 



stance as we see in many CyanophycetB,"m bacteria surrounded by 

 capsules, and in zooglea. The membrane then becomes extremely 



thick (Fig. 14, B). 



LOCOMOTIVE STRUCTURE. Most algae and fungi cannot move. 

 Many bacteria and all protozoa have more or less perfected locomotive 



structure. 



The Cyanophyeea and many bacteria, although without loco- 

 motive organs, present nevertheless oscillatory movements which seem 

 due to a general movement of the cytoplasm translated exteriorly 

 because of the flexibility of their membrane. With these exceptions, 

 movement is effected by means of a locomotive structure. 



This structure is found in its simplest 

 form in the pseudopodia of the amceba. 

 The naked cell of the amceba pushes out 

 pseudopods, simple expansions of the ecto- 

 plasm arising at any part of the body, 

 which take various shapes, and reenter the 

 body without leaving the least trace of their 

 existence. It is a result of motility of the 

 cytoplasm, one of its essential properties, 

 shown here exteriorly because of the absence 

 of a cellular membrane. 

 geard.) B, Thread of nostoc The locomotive structure is more com- 



la U gin o U u n s d case by " thkk mUd " P 1 ^ other protozoa; the pseudopod 



is replaced by contractile appendages- 

 flagetta, or mbratile cilia. 



The flagellum is a contractile appendage of definite shape and 

 position which draws the body after it by means of waving movements. 

 It is found on bacteria and flagellates. 



The organ of locomotion of bacteria is still little known (Fig. 15). 

 It consists of a certain number of contractile appendages placed at 

 one end of the cell, or at both, or sometimes distributed over the whole 

 body. These appendages, which may be called vibrating appendages, 

 have the characteristics of flagella. Their existence, for a long time 

 doubted, is now well established. 



The locomotive structure of the Flagellata is much better known. 

 It is characterized by one or more flagella inserted in the anterior 

 extremity of the cell. In case of more, one frequently folds back 



